Process and devices for sorting thermoplastic components from a mixed stream

ABSTRACT

Thermoplastic articles are removed from a mixed waste stream and are sorted by heating the articles along the path of the waste stream to different softening temperatures of the different types of articles before the articles contact the separating bodies which have surface formations that are forced into the softened zones of the thermoplastic article so that the articles are impaled upon the body. The articles are then removed. The force with which the softened articles are impaled is obtained by a support or counterforce member juxtaposed with the separating bodies.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/EP93/00509 filed 6 Mar. 1993and based upon German national application P 42 07 398.7 filed 9 Mar.1992 under the International Convention.

Our present invention relates to a process for separating thermoplasticcomponents from a mixed stream when sorting different types ofthermoplastic materials in contact with separating bodies; the inventionalso relates to devices for implementing the process.

BACKGROUND OF THE INVENTION

Different types of thermoplastic materials soften at differenttemperatures or within different temperature ranges. The changes in thephysical properties of the thermoplastic materials which take placeduring softening can be used for the sorting of plastic materials or forthe separation of plastic materials from materials such as glass ormetal. This problem arises particularly during recycling. For thispurpose plastic materials have to be selectively softened correspondingto their type and removed from the mixed stream by appropriate devices.

According to the state of the art thermoplastic components are sortedout from a mixed stream by bringing the mixed stream into contact with asufficiently heated separation surface, whereby the plastic componentsadhere to the separation surface due to the melting of their contactzones onto this surface. This removes the thermoplastic articles fromthe mixed stream and enables them to be subsequently scraped off (DE-3727 777 C2).

Since this separation principle relies on the adherent behavior ofplastic materials to be sorted which are softened to the point wherethey are almost melted and fluid, it is sensitive to contamination inpractice, such as during the recycling of plastic materials. Inherentwetness, residuals of the formerly contained goods or labels can hinderthe adhesion. The quantitatively interesting polyolefin plastics are bynature bad adhesives and therefore not very readily separated by thissorting method.

Furthermore in this process during operation the sorting surface isincreasingly covered by a layer of softened thermoplastics. This layerrenders the process less effective, on the one hand due to reduced heattransmission, and on the other hand due to the fact that as a result ofthe adhesive action of softened thermoplastic material, plasticcomponents which in themselves are not softened at the respectivetemperature and therefore are not among the target fraction, can stickto this layer. As a result the purity of the target fraction isquestionable.

In the separation process according to WO-A-88/000 98 the thermoplasticcomponents are not softened through selective heating and especially notin temperature zones which are specific to type. The components becomeadhesive due to the temperature of the metal surfaces they come incontact with and melt on the latter. The device required for carryingout the process is extremely complicated and expensive. It isparticularly hard to conceive how the pins or lances rotating togetherwith an eccentrically supported pin roller can be heated to be broughtprecisely to a certain temperature by the heating device inside a drum,so that previously unheated plastic components can melt on it whenpassing by.

A further drawback of this device working according to theunsatisfactory principle of separation based on adhesion is that it isnecessary to provide here special cleaning devices for the removal ofthe molten residuals of the plastic components from the heated surfaces.For this purpose a separate burner device for singeing the outer rollersurface is used, with subsequent brushing or another kind of removal ofthe remaining residuals.

U.S. Pat. No. 3,793,424 is based on the principle of separation throughadhesion or adhesive behavior of the plastic components. There it isindicated that the dry particles are fed to a heated, moving substrate,to which the plastic materials with a lower softening point adhere andthe particles with a higher softening point flow freely over it.

JP-A-54 022 477 can also classified as based on the unsatisfactoryprinciple of separation through adhesion. There, in the center of acollection chamber, is an electrically heated cylinder with a conicalend. Through that a plastic component is melted in a punctiform mannerand penetrates with the melt into the area of the collection chamber.The process comprises the following steps:

(a) local heating of a limited portion in the thermoplastic materialwith the conical end of a heating element with high thermalconductivity,

(b) this material is brought into contact with a second element oflesser thermal conductivity with a collection chamber,

(c) continuous heating of the material while a molten portion isintroduced into the enlarged space of the collection chamber, and

(d) cooling of the molten plastic material while it is introduced in thecollection chamber.

The corresponding device with individual, electrically heated meltingbodies and the respective collection bodies, partially traversed bycooling channels, assigned thereto is extremely complicated and prone tofailure, very difficult to control from the point of view of temperaturesetting and not suitable for an economical operation in view of thetime-consuming process steps (a) to (d). Consequently the plasticcomponents are not softened in defined temperature zone, but melt oncontact with heated bodies.

OBJECT OF THE INVENTION

It is the object of the invention to provide a process and a device forthe sorting of thermoplastic components from a mixed stream and for thesorting of different types of thermoplastic materials which overcomesthe drawbacks of separation based on adhesion and wherein the separationprinciple is no longer based on adherence or on the adhesive behavior ofthe softened thermoplastic material, but on a selective mechanicalanchoring on separating bodies with a special configuration.

SUMMARY OF THE INVENTION

In order to achieve this object in a process of the aforementioned kindthe invention provide that the plastic components are softened by beingheated in the mixed stream in temperature zones specific to type beforethey are picked up by the separating bodies, after which the softenedplastic components are affixed to the separating bodies which penetratethe softened surface of the plastic components or pierce the softenedsurfaces and then finally removed from the separating bodies.

Advantageously the process of the invention relies on a mechanicalfixation of the plastic components, in contrast to the unsatisfactoryseparation principle based on adherence or adhesive behavior. Separatingbodies either penetrate the sufficiently softened surface of the plasticcomponents or pierce this surface, whereby the plastic components aresecurely affixed and after that removed from the separating bodies bymechanical means. Plastic components of one type of plastics which aresufficiently softened at the applied process temperature so thatseparating bodies can penetrate their surface, are selected from othertypes of plastics whose structure has for instance not yet been softenedat the applied temperature. The same occurs also with foreign bodiessuch as made of metal, paper, ceramic or the like, which are not subjectto a selective softening through heating.

An embodiment of the invention provides that the penetration of theseparating bodies into the surface of the plastic components heatedspecifically to their type takes place under the influence of the forceof gravity.

Depending on the softening degree of the type of plastic to be selected,according to a further feature of the invention, it is possible effectthe penetration of the separating bodies into the surfaces of theplastic components softened by the heating specific to type by apressure force generated in a gap between the support surface and aseparating body.

Thereby one embodiment provides that the force required for thepenetration of the separating bodies into the surface of the plasticcomponents softened by heating specific to type is determined by theelastic yielding of the support surface or the separating body, as wellas by the size and shape of the plastic components. This makes possiblean extremely uniform setting and maintaining of the pressure forcegenerated in the gap between support surface an separating body.

Finally one embodiment of the process provides that the surface of theseparating bodies be coated with an anti-adhesive layer. This processstep is not complicated and results in a certain removal of the plasticparticles stuck to the separating bodies, this being the reason why thecontinuous condition of readiness of the separating bodies during thesorting process is maintained without change.

A device for implementing the process of the invention is characterizedby at least one separating body acting as conveyor, having a flat orcurved surface provided with structures for penetrating or piercing theplastic components which have been previously softened through selectivesoftening by applying heat specific to their type, as well as forsecuring the plastic components to the separating body and with meansfor the removal of plastic components affixed to the separating bodyafter they have been separated from the mixed stream, as well as withmeans for producing well defined temperature zones for the selectiveheating of the plastic components in the mixed stream prior to theirpickup by the separating bodies.

A particular advantage of this device is its extremely simpleconstruction. Thereby corresponding to the features of the dependentclaims embodiments can be provided wherein the structured surface of theseparating bodies is formed by grooves or knurls. Thereby the crests ofthe grooves or knurls can penetrate the softened plastic components andhold them. The grooved or knurled surfaces have the advantage that evencomparatively small plastic components, such as the ones occurringduring comminution processes, can be separated. Thereby the grooved orknurled surfaces can be roller surfaces.

According to one embodiment the separating bodies can be rollers, bandsor plates provided with bristles, needles, pins or lamellae. With thecorresponding selection of suitable surface structures of separatingbodies the person skilled in the art can optimize the sorting process ontarget depending on the materials to be separated.

In an embodiment of the invention the separating body forms a gap with asupport surface. Thereby the support surface can be a pressure roller ora passing conveyor belt, whereby the conveyor belt is pressed againstthe separating body at the location where support is needed by one ormore pressure rollers. The pressure rollers can be made of metal,plastic material or soft elastic materials such as rubber or foam, orcan have an inflatable rubber or plastic jacket in the shape of acylinder. The selection of the suitable material or combination ofmaterials is made with regard to the mechanical demands made on theseparating body.

Advantageously separating bodies can be provided with an anti-adhesivelayer, whereby on the one hand only strictly defined plastic componentscan be affixed due to the surface structure and on the other hand theaffixed plastic components can be completely removed when scraped off.Negative effects such as the adhesion of a thermoplastic layer to thesurface of the separating bodies are avoided due to the present of theanti-adhesive layer.

According to another feature of the invention several devices withsimilar or different construction are arranged in cascade one after theother. By arranging several devices according to the invention insuccession it is possible for instance due to targeted temperaturecontrol to perform a separation of various types in a single run.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a perspective view of a separating body of roller form;

FIG. 1A is a diagrammatic perspective view of another such body;

FIG. 1B is an end view of another separating body;

FIG. 1C is a side view of a separating body;

FIGS. 2A-2D are diagrammatic sectional views of separating bodies withdifferent surface structures;

FIG. 3 is a lateral view of a sorting device;

FIG. 4 is a lateral view of another sorting device;

FIG. 5 is a lateral view of a sorting device with elastic pressureroller;

FIG. 6 is a lateral view of a sorting device with separating roller andheated pins; and

FIG. 7 is a lateral view of three separating device arranged in acascade one under the other.

SPECIFIC DESCRIPTION

FIGS. 1, 1A, 1B and 1C show three separating bodies 4a, 4b and 4c,designed as rollers with different surface structures. The roller-shapedseparating body 4a is a so-called brushing roller with brush-likesurface structure 10a (FIG. 1A). The bristles forming the brushingsurface can be made of wire or very hard plastic wires. The separatingbody 4b has a surface 10b provided with pins. These pins 10b (FIG. 1)can be made out of heat-conductible materials such as copper, silver orbrass for the purpose of good heat conductivity and their length anddiameter are optimally adjusted to the sorting task at hand.

Finally FIG. 1C shows a lamellae roller 4c with circularly shapedlamellae.

The surface structure of the separating bodies 4a to 4c designed asrollers are optimally suited to the sorting task of different types forplastic materials. A basis therefor is the softening behavior ofthermoplastic materials, whereby these have a characteristic temperaturerange for each type of plastic, and when this range is reached theyconvert from the solid state to a softened, rubber-elastic state. Ifthere are several different types of plastic materials or othermaterials in a mix, then it is possible to selectively soften a chosentype of thermoplastic material through selective heating. In a mixedstream which can also contain hard materials as further components, suchsoftened thermoplastic materials have a fundamentally different elasticbehavior than the other components. The use of this difference in theelastic behavior for a selective fixation on the separating bodies 4a to4c. FIGS. 1, 1A, 1B and 1C or 14, 15, 16 (FIG. 7) provided by theinvention by means of structures at the separating bodies according tothe invention, represents the crux of the present invention.

In the case of pin or lamellar rollers 4b, 4c it is possible toelastically form or elastically fasten the pins or lamellae 10b or 10con the roller, so that they can individually adjust to the respectivedimensions of the components of the mixed stream. In a brush roller 4ait is possible to achieve the same through the elasticity of theindividual bristles 10a.

Advantageously separating bodies with a defined surface structure can beused. Such surfaces are represented purely schematically in FIGS. 2A-2Dand have similar comb-like cross sections 11a to 11d. These form surfacegrooves or knurls with more or less pronounced peaks. The groove edgescan penetrate the plastic material according to its degree of softeningand fasten the corresponding components. Grooved surfaces 11a to 11dhave the advantage that also small plastic parts, such as thoseresulting from a comminuting process, can be separated.

Separating bodies 4a to 4c, or separating bodies 14, 15, 16 can becomposed of different materials and combination of materials, e.g. ofsurface-coated metal, as long as they meet the thermal and mechanicalrequirements. It can for instance be advantageous to use separatingbodies made of material with good heat conductivity, because this wayheat required for the softening of the plastic material can be broughtto the contact zone.

FIGS. 3 to 6 show devices for the implementation of the method of theinvention with various embodiments. FIG. 3 shows a roller-shapedseparating body 4 with any desired surface structure. A conveyor belt 3guides from the left side a mixed stream 1 with various plasticcomponents and in certain cases foreign materials along a transport gap20 formed between the separating roller 4 and the conveyor belt 3. Thistransport gap 20 is created between two support rollers 2 guiding theconveyor belt 3 and the surface structure of the separating roller 4.Selectively heated plastic components 24 remain clinging to the surfacestructure of separating roller 4, and are scraped off by a doctor blade5 on the runoff left side and thrown into discharge trough 7. Theforeign matter parts not picked up by the separating roller 4 continueto remain on the conveyor belt and are collected at a differentlocation.

The device shown in FIG. 4 presents only unessential differences withrespect to the embodiment in FIG. 3. Instead of the comparatively longgap 20 between a support surface 21 formed by the conveyor belt 3 andseparating roller 4 in the embodiment according to FIG. 4 there iscomparatively short gap between the support roller 2 and the separatingroller 4.

FIG. 5 shows another embodiment of the device, whereby as support rollera gas-filled, highly elastic pressure roller 31 is used. The mixedstream is brought in from above through a feeding duct 8 and after ashort ride on the surface of separating roller 14 traverses the gap 20in an approximately vertical surface area between the separating roller14 and the elastic pressure roller 31. In this arrangement for instanceit is possible to heat the separating roller 14 from the inside, inorder to transport heat to the plastic components to be separated in themixed stream. In order to avoid a thermal overload of the elasticpressure roller 31, a cooling air flow 12 is provided, under whoseinfluence the surface temperature of the elastic pressure roller 31 isbalanced and kept at an acceptable level. Plastic components of one typeaffixed to the separating roller 14 are scraped off with the doctorblade 5 and thrown into the trough 7a. The parts of other plasticmaterials or foreign matter 25/27 which have not been picked up by theseparating roller 14 are thrown into the trough 7.

FIG. 6 shows a further variant of the device, wherein the separatingroller 14 has heated pins 10b. The conveyor belt 3 brings along plasticbottles 23 and other types of plastic materials or foreign matter 25/27underneath the separating roller 14. The latter is linked to anarticulation 41 via an approximately horizontal arm 40 and is relievedof weight in a manner known per se, for instance by a restoring elementor a counter-weight. As a result of this weight relief, the separatingroller 14 rolls with a precisely settable force over the components ofthe mixed stream, whereby the heated pins 10b penetrate a selectivelysoftenable type of plastic bottles 23 and transport those around withthe separating roller 14, until they are scraped off by the doctor blade5 and thrown into the discharge through 7. The plastic components orforeign matter 25/27 which could not be softened are transported by theconveyor belt to a further collection location. In this arrangement itis for instance possible to achieve a separation in the mixed stream ofhollow plastic bodies, such as plastic bottles, from non-plasticproducts, such as glass or metal containers. Compared to otherseparating processes based on the specific weight, the present processis not sensitive to residues of the contained goods. The pins 10b of theseparating roller 14 can be provided for this special purpose with abarb which assists the secure fixation, for instance of plastic bottles.These barbs also do not impair the scrape-off operation, because evenstronger affixed plastic parts can be scraped off with a sufficientlystable doctor blade.

In FIG. 7 for instance an arrangement is shown wherein due to thesuccession in cascade of several devices according to the invention,through targeted temperature control it is possible to achieve withoutproblems the separation of several different types 24, 25, 26 of plasticmaterial, as well as of foreign matter 27. From top to bottom,separating rollers 14, 15, 16 having the identical or differentstructures can be used. Each individual arrangement corresponds therebyto the embodiment according to FIG. 5, whereby in each case a separationgap 20, 20a, 20b is created between a separating roller 14, 15, 16 andthe corresponding elastic pressure roller 31 or a support surface 21,21a, 21b of a pressure belt 30, 30a, 30b. For the collection of theindividual types 24, 25, 26 of plastic material serve the troughs 7, 7a,7b, and intermediate materials are each guided through chutes 9 from anupper device to a device located therebelow.

The process and the devices according to the invention are notcomplicated, very suitable and safe to operate, and implement anextraordinarily economical method for sorting plastic materials duringrecycling. The invention thus proves to be a contribution to the reliefof the environment from waste, of great importance to the nationaleconomy.

We claim:
 1. A process for separating thermoplastic articles from amixed stream of articles and sorting different types of thermoplasticarticles from one another, said process comprising the steps of:(A)heating said thermoplastic articles in said mixed stream and indifferent temperature zones depending upon the article type torespective softening temperatures; (B) pressing surface formations ofrespective separating bodies into the respective thermoplastic articlesat the respective softening temperatures thereof while applying acounterforce to said articles against said separating bodies so thatsaid surface formations at least partially penetrate into the respectivearticles because of softening thereof but do not penetrate intononsoftened portions of other articles, thereby selectively impalingpenetrated articles on the respective separating bodies; (C) thereafterremoving impaled articles from the separating bodies; and (D) limitingadhesion of softened thermoplastic articles to said separating bodies bycoating same with an anti-adhesive coating.
 2. The process defined inclaim 1 wherein penetration of said separating bodies into thermoplasticarticles which have been softened is effected by a pressure forceexerted in a gap between each separating body and a support surfacejuxtaposed therewith.
 3. An apparatus for separating thermoplasticarticles from a mixed stream of articles and sorting different types ofthermoplastic articles from one another, said apparatus comprising:meansfor forming a mixed stream of articles including different types ofthermoplastic articles and displacing said mixed stream along a path;heating means along said path for heating said thermoplastic articles insaid mixed stream and in different temperature zones depending upon thearticle type to respective softening temperatures; separating bodiesdisposed along said path and juxtaposed with respective supports forpressing surface formations of respective separating bodies into therespective thermoplastic articles at the respective softeningtemperatures thereof by counterforce applied to said articles againstsaid separating bodies so that said surface formations at leastpartially penetrate into the respective articles because of softeningthereof but do not penetrate into nonsoftened portions of otherarticles, thereby selectively impaling penetrated articles on therespective separating bodies; means for thereafter removing impaledarticles from the separating bodies; and an antiadhesive coating on saidseparating bodies for preventing adhesion of said thermoplastic articlesto said separating bodies.
 4. The apparatus defined in claim 3 whereinsaid surface formations are pins.
 5. The apparatus defined in claim 3wherein said surface formations are bristles.
 6. The apparatus definedin claim 3 wherein said surface formations are lamellae.
 7. Theapparatus defined in claim 3 wherein said surface formations are formedby knurls and grooves.
 8. The apparatus defined in claim 3 wherein saidseparating bodies are rollers.
 9. The apparatus defined in claim 3wherein said support is formed by a belt.
 10. The apparatus defined inclaim 3 wherein said support is an inflatable member deformed by saidmixed stream.